The objective of the proposed project is to examine (1) the role of abnormalities in skeletal muscle basal glucose metabolism, and (2) the role of altered insulin dependence in the development of the apparent peripheral insulin resistance in the genetically obese-diabetic mice (db/db). The perfused mouse hemicorpus preparation will be used to measure glucose utilization, glucose transport activity, glucose phosphorylation, and insulin degradation. These parameters and their dependence on insulin will be studied in control and db/db mice at various ages in order to determine the age of onset and the course of development of abnormalities. The glucose transport process will be examined by using minimally metabolized sugars in "washout" experiments, glucose phosphorylation will be studied by following 3H2O production from (2-3H) glucose, and glycolytic activity will be measured by the production of 3H2O from (5-3H) glucose as well as lactate plus pyruvate accumulation. Insulin degradation will be followed by immunoassays carried out in influent and effluent medium. In vivo glucose oxidation, glucose turnover, and lipogenesis will be studied with mdb/mdb mice prior to weaning (8-28 days after birth) to delineate the time of onset of derangements detected in the youngest db/db mice (4 weeks of age), that may play roles in the development of hyperinsulinemia, insulin insensitivity, and obesity.